The present invention relates generally to a zoom lens, and more particularly to a high-zoom-ratio zoom lens including a wide-angle range.
Today's mainstream high-zoom-ratio zoom lenses for digital camera purposes are of the type comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power. Patent publications 1 and 2 have come up with a zoom lens of the type where the first lens group is allowed to move toward the object side, thereby achieving high performance well fit especially for an image pickup device that has a zoom magnification of 8 or greater and a decreased pitch.
However, the zoom lens of patent publication 1 still fails to achieve a wide-angle arrangement, because its half angle of view is barely 30° at the wide-angle end. Patent publication 2, on the other hand, is prima facie satisfactory in terms of a wide-angle arrangement, because its half angle of view is of the order of 35° at the wide-angle end. Still, it fails to have any sufficient back focus at the wide-angle end with a limited space for focusing, rendering it difficult to keep the angle of incidence of light on an image pickup device CCD substantially parallel. To achieve ever higher performance and ever higher zoom ratios, it is thus necessary to reassess the refracting power layout of each lens group.
Patent Publication 1
JP(A)11-109241
Patent Publication 2
JP(A)2001-350092